1. Field of the Invention
The present invention is directed generally to instruments for conducting range of motion evaluations and, more specifically, to instruments for conducting range of motion evaluations of joints.
2. Description of the Background
Evaluation of the hands and the larger upper extremities, as currently performed in clinics and hospitals, consists of measurements of strength, range of motion, nerve sensation and graphic depiction of deformities of the hand, arm and shoulder. These measurements are required for pre-operative, post-operative, and periodic assessment of functional abnormality. To meet the requirements of most health and workman's compensation insurance, these measurements are standardized and reported in a consistent format throughout the United States. Evaluation techniques in other countries are quite similar, with expected changes in measurement units and reporting format.
Sufficient range-of-motion of any joint is critical for functionality. Because of the importance of range-of-motion, every joint has at least one measurement, and several have more than one measurement such as the wrist and shoulder. Measurements are typically compared between an injured and non-injured joint. These measurements can also be used to calculate an impairment rating for the particular joint or joints being evaluated. The impairment rating consists of a mathematical formula for calculating the usefulness of the joint or extremity being evaluated, given as a percent of being fully functional. The standard formula for calculating impairment ratings is set forth in the 1989 American Medical Association Guides to the Evaluation of Permanent Impairment.
In general, the goniometer is used to measure range-of-motion of the joints. In the present state of the art, goniometers generally consist of two (2) thin, flat members or halves of rigid or semi rigid material which rotate about a common axis. One member has indicia for determining its angular relationship with the other. Therefore, aligning one member with one bone from the joint being evaluated and aligning the other member with the other bone of that joint, the angular relationship of the bones can be read from the indicia printed on the first member. By making successive measurement of this type, the range of motion of the joint is determined.
In most cases, goniometers of this design are constructed of clear or translucent plastic, or of sheet metal. Thickness varies between 0.040 inches up to about 0.125 inches for each piece. The sizes vary greatly from small goniometers to measure the joints of the hand to large goniometers to measure the shoulder and elbow. The information printed onto these goniometers is in angular gradations from zero degrees to three hundred sixty, with increments of one, two or five degrees being typical. These goniometers have no function other than rotation of the two halves about their pivot axis from which the angular relationship of these two halves is determined. Examples of such state of the art goniometers include the PC 50 series goniometers manufactured under the Jamar.RTM. name by J. A. Preston Corporation, 60 Page Road, Clifton, N.J. 07012. Another example is the 6 inch plastic goniometer manufactured by North Coast Medical, Inc., 450 Salmar Avenue, Campbell, Calif. 95008.
Another type of goniometer recently introduced is the digital goniometer. This design is virtually the same as those described above, except it includes rotation sensing technology to produce a digital LCD readout of the angle between the two (2) halves. This type typically has a moving zero point, data storage, and a computer interface output in addition to the digital LCD readout. A battery provides electrical power. This type is generally constructed of molded plastic and metal parts and includes a circuit board containing the necessary electronic components for rotation sensing, the LED display and computer interface. An example of this type of goniometer includes Guymon Model 01129 Goniometer manufactured by J. A. Preston Corp.
Because of the importance of range of motion to physiological well-being, it is important that range of motion measurements not only be accurate, but be repeatedly accurate. Accuracy is important to determine in absolute terms the exact degree of motion impairment and to measure the degree of improvement (or the lack thereof) over time or as treatments are administered. The results of range of motion measurements are critical to evaluation of actual loss of function, which in turn is critical to resolution of health insurance and workman's compensation claims. These measurements are also critical to determining the proper and most appropriate treatment.
Using the goniometers currently available such as those described above, it is common for errors in the range of motion measurement to typically be on the order of 2 to 5% from one measurement to the next by the same examiner and on the order of 5 to 10% from one measurement to the next by different examiners. There is therefore a need for a goniometer design that reduces to a minimum both intra-examiner and inter-examiner error. There is also a need for a goniometer which reduces the risk of error in transcription of the angular measurement read, and errors induced by the pain felt by the patient during the measurement process, either from the presence of the goniometer being brought too close to injured tissue or from injured/deformed extremities interfering with the configuration of the goniometer. There is also a need for a goniometer which is easily and accurately aligned with the center line of the bones of the joint being measured. Finally, there is a need for a goniometer which minimizes errors induced by manipulation of the goniometer itself.